A scroll compressor may include in a known manner:                a scroll compression device including a fixed scroll element having a fixed base plate and a fixed spiral wrap extending from the fixed base plate, and an orbiting scroll element having an orbiting base plate and an orbiting spiral wrap extending from the orbiting base plate, the orbiting scroll element being configured to perform an orbiting movement in relation to the fixed scroll element, the fixed and orbiting scroll elements intermeshing with each other and delimiting compression chambers,        a sealing device arranged in an end face of the fixed spiral wrap of the fixed scroll element and having a sealing surface sealingly cooperating with the orbiting base plate of the orbiting scroll element,        a sealing device arranged in the end face of the orbiting spiral wrap of the orbiting scroll element and having a sealing surface sealingly cooperating with the fixed base plate of the fixed scroll element,        a drive shaft configured to drive the orbiting scroll element in an orbiting movement,        at least one bypass passage arranged to communicate an intermediate pressure chamber with a discharge pressure chamber, and        at least one bypass passage valve, also named intermediate discharge valve, provided on the fixed base plate of the fixed scroll element and movable between a closing position in which the at least one bypass valve closes the at least one bypass passage and an opening position in which the at least one bypass valve opens the at least one bypass valve bypass passage.        
When the at least one bypass valve is subject, on its face directed towards the fixed base plate of the fixed scroll element, to a pressure below the pressure in the discharge pressure chamber, the at least one bypass valve is maintained in the closing position and isolates the intermediate pressure chamber from the discharge pressure chamber. In this case, the compression rate, also named pressure ratio (ratio between the pressure at the discharge outlet of the scroll compressor and the pressure at the suction inlet of the scroll compressor), of the scroll compressor is maintained at its maximum value.
When the at least one bypass valve is subject, on its face directed towards the fixed base plate of the fixed scroll element, to a pressure above the pressure in the discharge pressure chamber, the at least one bypass valve resiliently deforms towards the opening position and puts the intermediate pressure chamber in communication with the discharge pressure chamber. Therefore at least a portion of the refrigerant compressed in the scroll compression device is discharged towards the discharge pressure chamber through the at least one bypass passage before this portion of the refrigerant reaches a discharge port located at a center portion of the fixed and orbiting scroll elements.
Consequently, the presence of the at least one bypass passage and of the at least one bypass valve allows to reduce, depending on the seasons, the pressure ratio of scroll compression device, and consequently to limit overcompression of the refrigerant. Such a limitation of the refrigerant overcompression improves the energy efficiency of the scroll compression device.
However, the presence of the at least one bypass passage and of the at least one bypass valve significantly increases the global cost of the scroll compression device, and requires an adjustment of the displacement of the scroll compression device. Further the installation of the at least one bypass valve on the fixed scroll element could be difficult.
Furthermore, the at least one bypass passage can only be optimized for a specific pressure ratio, and does not allow a wide efficiency optimization of the scroll compressor for all its operating conditions. Moreover, the discharge section of the at least one bypass passage is limited, and thus does not allow an optimal limitation of the overcompression of the refrigerant.
Moreover, the presence of the at least one bypass passage could decrease the stiffness of the fixed scroll element which generally includes said at least one bypass passage, or leads to an increase of the mass of the fixed scroll element to keep the same stiffness.